Method of producing compositions containing mineral aggregates



March 5, 1 c R R O D METHOD OF PRODUCING COMPQSITIONS CONTAINING MINERAL AGGREGATES Filed July 22, 1926 v INVENTOR hot by spreading on Patented Mar. 5, 1929.

UNITED STIA TES CRAIG R. ARNOLD, OF DAHLONEGA, GEORGIA.

METHOD OF IRODUCING COMPOSITIONS CONTAINING MINERAL AGGREGATES.

Application filed July 22,

My invention relates to the method of producing combinations of asphalt or other bituminous binder with aggregates or sub-divided mineral matter adapted for use in road work or for other surfacing operations such as for paving, flooring, roofing or other processes.

My invention may be utilized in producing a composition adapted for transportation and use cold as, described in a co-pending application of Joseph E. Boyd or may be employed in producing a mixture or composition of bituminous material like asphalt in a fluid state with the aggregates where the mixture is designed to be utilized while still the surface to be protected and compressed by a roller or otherwise.

According to a practice heretofore frequently employed for producing such com- ;positions the materials-have been mixed in desired proportions of asphalt or other bituminous binder material in fluid condition and heated aggregates and other ingredients by dumping into a pug mill and stirring while heated and then dumping the mixture into a transporting vehicle while very hot, say 350 F. and blanketing to retain the heat. The material while hot is spread and rolled to make the usual sheet asphalt pavement, surface for roads, Walks, roofs and other uses.

If the aggregates are coarse they readily retain the heat and this method is satisfactory although expensive.

To make the sheet when laid more durable it is desirable to add a predetermined amount of filler generally composed of dust lime stone, clay dust etc. although Portland cement can and is often used on account of its fineness although rather expensive.

When either of these fillers are used or in fact anypther filler. this is liable to become ba-lled up and when rolled out makes a sore or weak spot on the surface. To overcome this detect it has been proposed to use a cylinder which revolves, and to force the liquid hot asphalt into the mass under a pressure and revolve the mass for a predetermined period to mechanically mix or stir the mass in the presence of the asphalt while under pressure. The method overcomes the trouble of balling up the fillers etc. but produces endless other troubles.

It is mechanically diiiicult to pump the hot asphalt under pressure while moreover the 1926. Serial-N0. 124,134.

cylinder is liable to leak and cause losses. The occluded gases etc. become compressed and tend to insulate the particles which rcv duces the efliciency of the method.

I propose to reverse these conditions by exhausting the air in the mixing cylinder during the mechanical mixing or stirring of the contents in the presence of the asphaltici' binder by maintaining a partial vacuum which has several advantages over plenum. It exhausts all the air or partially so, it draws the heated asphalt into the mixing cylinder so that it doesnt clog, and the door through which the materials are introduced is more readily sealed by the outside pressure than with a pressure within. v

After the charge is thoroughly mixed it may be utilized in any desired manner. If employed in connection with the Boyd process hereinafter mentioned the charge may be dumped onto a screen which shakes it into small particles which-land on a moving belt conveyor long enough to cool off, a spra of water being applied to hasten the coo ing process if desired especially in warm weather.

Various devices as Well understood by those skilled in the art are available for practicing my invention. ln the drawings I have illustrated a general-form of apparatus that may be employed.

In said drawings 1 indicates a revolving cylinder or mixing chamber of a pug mill having suitable stirring devices and 2 indicates a pipe or conduit entering the cylinder arranged coaxially with the axis of revolution of the cylinder to deliverthe hot asphalt or other bituminous material in liquid condition to the cylinder. 3 indicates a similar pipe by means of which a partial vacuum may be produced within the cylinder. 4 is a series .of screens diminishing in size of mesh from the top to the bottom screen and providcd with means for shaking or agitating them when the mixed material is dumped onto the topmost screen fromthe mixing cylinder, and 5 is a belt conveyor receiving the particles or granulations separated from one another by the screening operation and by means of which they are conveyed to delivery point for storage or shipment. 6 indicates any suitable means for applying a spray-of water or other fluid or liquid to the mateiral on the belt or as it drops from the screen to hasten the cooling process. 7 is an exhaust pump connected to pipe 3 and 8 is a hopper from' which the aggregate and other material may be dropped into the mixing cylinder or chamber through an opening in the latter adapted to be sealed. 4

W hat- I claim as my invention is:

1. The herein described improvement in producing a compound of bituminous material in fluid condition and suitable aggregates consisting in mechanically mixing or stirring the aggregates in the presence of the bituminous material While hot in a suitable container wherein a partial 'vacuum is main tained during the mixing operation.

2. The herein described method of producing an asphaltic composition containing mineral aggregates and a filler consisting in mixing the hot asphalt with the mineral aggregates by a mechanical stirring operation in' a suitable container wherein a partial. vacuum is maintained during the mixing operation.

'3. The herein described improvement in tile-111 in a suitable pug mill or container from which the air is exhausted to cause the heated binder to be drawn mixing operation. a 4. The herein described improvement in producing compositions of asphalt or other bituminous material and finely divided aggregates consisting in placing the same in a revolving container to Which the hot asphalt or bituminous material is supplied and maintaining a partial vacuum in said container While it revolves to prevent the materials from balling up during the mixing operation.

Signed at New York in the county of New York and State of New York this 8th day of into the same during the July A. D. 1926.

CRAIG R. ARNOLD. 

